title: Permanent El Niño during the Pliocene warm period not supported by coral evidence.
abstract: The El Niño/Southern Oscillation (ENSO) system during the Pliocene warm period (PWP; 3-5 million years ago) may have existed in a permanent El Niño state with a sharply reduced zonal sea surface temperature (SST) gradient in the equatorial Pacific Ocean. This suggests that during the PWP, when global mean temperatures and atmospheric carbon dioxide concentrations were similar to those projected for near-term climate change, ENSO variability--and related global climate teleconnections-could have been radically different from that today. Yet, owing to a lack of observational evidence on seasonal and interannual SST variability from crucial low-latitude sites, this fundamental climate characteristic of the PWP remains controversial. Here we show that permanent El Niño conditions did not exist during the PWP. Our spectral analysis of the δ(18)O SST and salinity proxy, extracted from two 35-year, monthly resolved PWP Porites corals in the Philippines, reveals variability that is similar to present ENSO variation. Although our fossil corals cannot be directly compared with modern ENSO records, two lines of evidence suggest that Philippine corals are appropriate ENSO proxies. First, δ(18)O anomalies from a nearby live Porites coral are correlated with modern records of ENSO variability. Second, negative-δ(18)O events in the fossil corals closely resemble the decreases in δ(18)O seen in the live coral during El Niño events. Prior research advocating a permanent El Niño state may have been limited by the coarse resolution of many SST proxies, whereas our coral-based analysis identifies climate variability at the temporal scale required to resolve ENSO structure firmly.
authors.affiliation: Department of Natural History Sciences, Faculty of Science, Hokkaido University, Sapporo 060-0810, Japan. nabe@mail.sci.hokudai.ac.jp
authors.forename: Tsuyoshi
authors.initials: T
authors.lastname: Watanabe
authors.forename: Atsushi
authors.initials: A
authors.lastname: Suzuki
authors.forename: Shoshiro
authors.initials: S
authors.lastname: Minobe
authors.forename: Tatsunori
authors.initials: T
authors.lastname: Kawashima
authors.forename: Koji
authors.initials: K
authors.lastname: Kameo
authors.forename: Kayo
authors.initials: K
authors.lastname: Minoshima
authors.forename: Yolanda M
authors.initials: YM
authors.lastname: Aguilar
authors.forename: Ryoji
authors.initials: R
authors.lastname: Wani
authors.forename: Hodaka
authors.initials: H
authors.lastname: Kawahata
authors.forename: Kohki
authors.initials: K
authors.lastname: Sowa
authors.forename: Takaya
authors.initials: T
authors.lastname: Nagai
authors.forename: Tomoki
authors.initials: T
authors.lastname: Kase
mesh_terms: D000818:Animals; D037421:Anthozoa / Q000378:metabolism; D001272:Atmosphere; D002980:Climate; D059000:El Nino-Southern Oscillation / Q000266:history*; D019277:Entropy; D005580:Fossils; D049690:History, Ancient; D010103:Oxygen Isotopes; D010140:Pacific Ocean; D010679:Philippines; D054712:Salinity; D012621:Seasons; D012623:Seawater / Q000032:analysis; D013696:Temperature; D013997:Time Factors
chemical_list: D010103:Oxygen Isotopes